I mainly play adventure games (think: Monkey Island, Broken Sword, etc.). I was browsing the Mac Game Store app and came across a game called Deponia. It requires a CPU speed of 2 Ghz and I'm using a 2012 1.8 Ghz i5 MBA with 4 GB RAM. I meet all the other requirements; it only requires 2 GB RAM. Is the .2 Ghz less of processing power enough that I really can't run the game as I know MBA have the TurboBoost capability that would put it over the system requirements for the game.

Amount of ram, gpu, and cpu family are the main factors that will make a game to run or not. A few Mhz difference will hardly stop you from running a game. Just make sure the 3 aforementioned factors are ok. The most suspicious one would be the intel integrated graphics gpu.